/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.index.processor;

import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;

/**
 * A {@link StereotypesProvider} implementation that extracts the stereotypes
 * flagged by the {@value INDEXED_ANNOTATION} annotation. This implementation
 * honors stereotypes defined this way on meta-annotations.
 *
 * @author Stephane Nicoll
 * @since 5.0
 */
class IndexedStereotypesProvider implements StereotypesProvider {

    private static final String INDEXED_ANNOTATION = "org.springframework.stereotype.Indexed";

    private final TypeHelper typeHelper;


    public IndexedStereotypesProvider(TypeHelper typeHelper) {
        this.typeHelper = typeHelper;
    }


    @Override
    public Set<String> getStereotypes(Element element) {
        Set<String> stereotypes = new LinkedHashSet<>();
        ElementKind kind = element.getKind();
        if (kind != ElementKind.CLASS && kind != ElementKind.INTERFACE) {
            return stereotypes;
        }
        Set<Element> seen = new HashSet<>();
        collectStereotypesOnAnnotations(seen, stereotypes, element);
        seen = new HashSet<>();
        collectStereotypesOnTypes(seen, stereotypes, element);
        return stereotypes;
    }

    private void collectStereotypesOnAnnotations(Set<Element> seen, Set<String> stereotypes, Element element) {
        for (AnnotationMirror annotation : this.typeHelper.getAllAnnotationMirrors(element)) {
            Element next = collectStereotypes(seen, stereotypes, element, annotation);
            if (next != null) {
                collectStereotypesOnAnnotations(seen, stereotypes, next);
            }
        }
    }

    private void collectStereotypesOnTypes(Set<Element> seen, Set<String> stereotypes, Element type) {
        if (!seen.contains(type)) {
            seen.add(type);
            if (isAnnotatedWithIndexed(type)) {
                stereotypes.add(this.typeHelper.getType(type));
            }
            Element superClass = this.typeHelper.getSuperClass(type);
            if (superClass != null) {
                collectStereotypesOnTypes(seen, stereotypes, superClass);
            }
            this.typeHelper.getDirectInterfaces(type).forEach(
                    i -> collectStereotypesOnTypes(seen, stereotypes, i));
        }
    }

    private Element collectStereotypes(Set<Element> seen, Set<String> stereotypes, Element element,
                                       AnnotationMirror annotation) {

        if (isIndexedAnnotation(annotation)) {
            stereotypes.add(this.typeHelper.getType(element));
        }
        return getCandidateAnnotationElement(seen, annotation);
    }

    private Element getCandidateAnnotationElement(Set<Element> seen, AnnotationMirror annotation) {
        Element element = annotation.getAnnotationType().asElement();
        if (seen.contains(element)) {
            return null;
        }
        // We need to visit all indexed annotations.
        if (!isIndexedAnnotation(annotation)) {
            seen.add(element);
        }
        return (!element.toString().startsWith("java.lang") ? element : null);
    }

    private boolean isAnnotatedWithIndexed(Element type) {
        for (AnnotationMirror annotation : type.getAnnotationMirrors()) {
            if (isIndexedAnnotation(annotation)) {
                return true;
            }
        }
        return false;
    }

    private boolean isIndexedAnnotation(AnnotationMirror annotation) {
        return INDEXED_ANNOTATION.equals(annotation.getAnnotationType().toString());
    }

}
